Method for fabricating dental bridges dental crowns and corono-radicular retainers

ABSTRACT

The invention improves the main one in the U.S. Pat. No. 3,636,632 issued Jan. 25, 1972 and refers to the elimination of possible adjustments of the occlusal surfaces, in the following way: - IN THE CASE OF DENTAL BRIDGES AND DENTAL CROWNS, BY THE REPLACEMENT OF THE SMALL REMOVABLE MODEL, WHICH COMPRISED THE TOOTH-STUMP AND THE ALVEOLARY CREST ZONE, BY A REMOVABLE MODEL, COMPRISING THE ADJOINING TEETH, WHICH SLIDES IN AN EXTENDED MODEL, MADE OF HARD PLASTER, WHICH COMPRISES, TOO, THE TOOTHSTUMP AREA OND THE ALVEOLARY CREST ZONE; - IN THE CASE OF COMPLETELY METALLIC OR MIXED SEMIPHYSIOGNOMICAL FULL CROWNS, IT USES A COMPLEX, CONSISTING OF MOBILE TOOTHSTUMPS, MADE OF HARD PLASTER, FASTENED TO A PLASTIC SUPPORT, WHICH COMPLEX SLIDES, IN ITS TURN, IN AN EXTENDED PLASTER MODEL; - IN THE CASE OF DENTAL BRIDGES, WITH CONSTITUTING ELEMENTS, CONSISTING OF ONE OR SEVERAL CORONO-RADICULAR RETAINERS AND FULL CROWNS, THESE ARE MADE, SIMULTANEOUSLY, WITH THE BRIDGE BODY, BY CASTING WITH CONTROLLED THICKNESS. In all three cases, the invention uses duplicated models, realized in investment material, suitable for chrome-cobalt alloys, by means of negative impressions, made of reversible hysrocolloid. On these duplicated models is realized the wax pattern, by applying a wax strip of suitable thickness, on both the coronoradicular retainers and the dental crowns; subsequently, a lid of the same wax is applied on these, the pattern of the bridge body is assembled with them, constituting, ultimately, the pattern of the whole dental bridge; then follows the one-piece casting of the pattern from chrome-cobalt alloys.

United States Patent [191 Costa et al.

[ Sept. 16, 1975 METHOD FOR FABRICATING DENTAL BRIDGES, DENTAL CROWNS AND CORONO-RADICULAR RETAINERS [75] Inventors: Eugen Costa; Lucian Ene; Stelica Dumitrescu; lon Covaci, all of Bucharest, Romania [73] Assignee: Policlinica de Stomatologie Protetica a Muncipiului Bucuresti, Bucharest, Romania [22] Filed: Oct. 19, 1972 [21] Appl. No.: 299,017

Related U.S. Application Data [63] Continuation of Ser. No. 70,444, Sept. 8, I970.

Primary Examiner-Robert Peshock Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [5 7] ABSTRACT The invention improves the main one in the U.S. Pat. No. 3,636,632 issued Jan. 25, 1972 and refers to the elimination of possible adjustments of the occlusal surfaces, in the following way:

in the case of dental bridges and dental crowns, by the replacement of the small removable model, which comprised the tooth-stump and the alveolary crest zone, by a removable model, comprising the adjoining teeth, which slides in an extended model, made of hard plaster, which comprises, too, the tooth-stump area ond the alveolary crest zone;

in the case of completely metallic or mixed semi-physiognomical full crowns, it uses a complex, consisting of mobile toothstumps, made of hard plaster, fastened to a plastic support, which complex slides, in its turn, in an extended plaster model;

in the case of dental bridges, with constituting elements, consisting of one or several corono-radicular retainers and full crowns, these are made, simultaneously, with the bridge body, by casting with controlled thickness.

In all three cases, the invention uses duplicated models, realized in investment material, suitable for chrome-cobalt alloys, by means of negative impressions, made of reversible hysrocolloid.

On these duplicated models is realized the wax pattern, by applying a wax strip of suitable thickness, on both the corono-radicular retainers and the dental crowns; subsequently, a lid of the same wax is applied on these, the pattern of the bridge body is assembled with them, constituting, ultimately, the pattern of the whole dental bridge; then follows the one-piece casting of the pattern from chrome-cobalt alloys.

5 Claims, 56 Drawing Figures PMENTEB SEP I 6 I975 SHEET 2 or 5 METHOD FOR FABRICATING DENTAL BRIDGES DENTAL CROWNS AND CORONO-RADICULAR RETAINERS This is a continuation of application Ser. No. 70,444, filed Sept. 8, 1970.

The present invention improves and extends the main invention with the US. Pat. No. 3,636,632 issued Jan. 25, 1972, entiteld Method for the fabrication of dental bridges, crowns and corono-radicular retainers" and refers to an improved fabricating method from base alloys (chrome-cobalt alloys), as well as to the extention of the invention, by that it enables the production of bridges, whose constituting elements consist of radicular retainers, crowns and bridge body, by one-piece casting and with controlled thickness.

The main invention uses in a first variant, in the case of dental bridges, a small removable model, made of hard plaster, of reduced size, comprising the stumps area and the alveolary crest zone, which model slides in an extended model of plaster in a second variant, in the case of entirely metallic or mixed semiphysiognomical dental full crowns, mobile stumps, made of hard plaster, which are siding, too, in an extended model of plaster, and, in a third variant, in the case of corono-radicular retainers, a model of hard plaster of cylindrical shape, with the impression of the root-canal, in the first and second versions, both the small removable model and the mobile stumps, respectively, being duplicated, fashioned into a reduced anatomical form, in order to realize them in investment material, while in the third variant, the hard plaster model of cylindrical shape, with the impression of the root canal, is duplicated in order to obtain it in investment material, by means of a metallic taper dowel with threaded head, which is introduced into the root canal impression, this complex being fastened, by means of a threaded screw, to the lid of a former, the negative impression from reversible hydrocolloid of the corono-radicular retainer being obtained, after the removal of the hard plaster model, the pattern being realized on the duplicated model from investment material, by the application of a wax band of suitable thickness (for instance, 0.4 mm), this operation being followed, finally, after the obtention of the mould, in all the three variants mentioned above, by the casting of the metal.

The fabricating method of dental bridges, crowns and corono-radicular retainers, according to the above main invention, has the disadvantage that the small removable model, comprising the stumps area and the alveolary crest zone, leads to a relative accuracy, which results in a difficult adaptation in the buccal cavity, at the level of occlusal surface, due to the fact that in the technological process intervenes the initial hygroscopic and thermal expansion of the small removable models, realized in investment material.

Also, in the case of completely metallic or mixed semiphysiognomical dental crowns, the main invention presents the drawback that the mobile stumps of hard plaster. duplicated by means of a negative impression, of reversible hydrocolloid, obtained from investment material, to which is added also the initial thermal dilatation, in order to compensate the contraction of the metal, leads to arelative adaptation of the duplicated stump, which slides in the extended plaster model, just as in the case ofone-piece cast bridges, it being formed, finally, that at the level of the occlusalsurface, some modifications occur, represented by the rise of the occlusion, at the moment of the application of the finished crowns in the buccal cavity.

The present invention improves the main invention, in that it replaces in order to avoid adjustments at the acclusal surfaces in the case of dental bridges the small removable model of hard plaster (used in the main invention), which comprises the area of dental stumps and the alveolary crest zone and which slided in an extended model of plaster, using in the present invention, a removable plaster model, including the adjoining teeth and which slides, too, in an extended model of 'hard'plaster, that comprises the coronary stumps area and'the alveolary crest zone. In the case of completely metallic or mixed semi-physiognomical dental full crowns, the present invention uses a complex, consisting of mobile tooth-stumps of hard plaster, fixed on a plastic support, which complex slides, in its turn, in an extended model of plaster.

In the case of both dental bridges and dental crowns, both the extended model of hard plaster and the mobile stumps, fixed on a support of plastic material, are duplicated, both models, with the tooth stumps, being fashioned in a reduced anatomical shape, in order to realize them from investment material, by means of a negative impression from reversible hydrocolloid.

The fashioning of the pattern is carried out by applying a wax strip of suitable thickness, for instance, 0.4 mm, on the investment duplicated model.

After the final realization of the wax pattern and obtention of the mould, this operation is followed, finally, in the case both of dental bridges and mixed semiphysiognomical full crowns, by the casting of the chrome-cobalt alloy.

Another purpose of the same improved invention refers to its extension for the fabrication of dental bridges, whose constituting elements consist of one or several corono-radicular retainers and full crowns, realized simultaneously in one piece with the bridge body, by casting, with controlled thickness.

In this case, too, a removable plaster model is used, which includes the adjoining teeth and which slides, too, in an extended model of hard plaster, which comprises the tooth-stumps area and the impression of the root-canals, as well as the alveolary crest zone.

This plaster model is duplicated after the toothstump is formed; one of the constituting elements was fashioned in a reduced anatomical shape, while in the root-canal impression a metallic taper dowel, provided with an internally threaded head, was introduced, forming a complex which is fastened to the lid of a former, by means of a threaded screw, where the reversible hydrocolloid is poured. After this, the extended model of hard plaster is removed from the reversible hydrocolloid, obtaining a negative impression, into which an investment material, suitable for the chromecobalt alloy, is poured.

The threaded screw is unscrewed from the former lid, and the reversible hydrocolloid is taken out from the former, in order to enable the removal of the latter, obtaining ultimately, the investment duplicated model.

On the investment duplicated model, the wax pattern is realized, by applying a band of suitable thickness, for instance, 0.4 mm, as above, on both the coronoradicular retainer and the dental crown, after which one applies on the occlusal surface of the dental crown and on the corono-radicular retainer, a lid made of the same wax, in order to fashion the occlusal relief of the crown, as well as for the realization of the coronoradicular retainer pattern.

The pattern of the bridge body is united with the full crown and with the corono-radicular retainer, respectively, constituting, ultimately, the pattern of the whole dental bridge.

After the final realization of the pattern and obtention of the mould, this operation is followed by the casting of the chrome-cobalt alloy.

Three examples are further given, for the application of the method according to the improvement and extension of the invention, in connection also with FIGS.

I 36 a, b, which represent:

FIG. 1 a longitudinal section through the impression complex, in which one can observe the stump impressions, covered with copper rings and thermoplastic material, over which the plaster super-impression was taken;

FIG. 2 a longitudinal section of the impression complex into which plaster was poured, comprising the adjoining teath area, with the aim of obtaining the removable model of the adjoining teeth;

FIG. 3 a longitudinal section through the whole impression complex and of the extended model of hard plaster, after the pouring of the hard plaster, into the stumps impression and of the edentate zone between the stumps, for the obtention of the complex model;

FIG. 4 a longitudinal section of the complex model after the removal of the mould of the complex impression of plaster, on which one can see the stumps covered with copper rings and thermoplastic material, as well as the removable plaster model of the adjoining teeth;

FIG. 5 a longitudinal section of the complex model, after the taking out of the copper rings and the removal of the thermoplastic material;

FIG. 6 a longitudinal section of the complex model, with the tooth stumps, reconstituted in a reduced anatomical shape with wax mixture, consisting of wax and guttapercha;

FIG. 7 a longitudinal section of the complex model of hard plaster, with the tooth-stumps, reconstituted in a reduced anatomical shape, fastened, without the removable model of plaster of the adjoining teeth, to the lid of a former;

FIG. 8 a longitudinal section through the negative (mould), obtained in reversible hydrocolloid, of the complex model of hard plaster;

FIG. 9 longitudinal section through the negative (mould), from reversible hydrocolloid, into which investment material was poured, for the obtention of the investment duplicated complex;

FIG. 10 a longitudinal section through the invest ment complex model, on which slides the plaster model of the adjoining teeth;

FIG. ll a longitudinal section through investment complex model and the removable plaster model of the adjoining teeth, on the tooth-stumps being applied suitable wax, constituting thus the pattern of the crowns, together with the pattern of the bridge body, realising also a contact point with the adjoining teeth;

FIG. 12 a, h, c, d longitudinal sections through the pattern model, on which the casting rods have been applied, being removed the parts of no interest of the investment model, as well as the removable plaster model of the adjoining teeth;

' FIG. 13 a a longitudinal section through a complex of model pattern, provided with a casting funnel, with a central canal, which complex is located on the base of a former, on which the cylinder of the former has been applied, with the aim of obtaining the mould of investment material;

FIG. 13 b a cross section through the AA plane of FIG. 13 a, of the model-pattern complex, after the obtention of the mould;

FIG. 14 a longitudinal section through the complex model of plaster, on which are sliding the mobile teeth-stumps, fixed on plastic supports;

FIG. 15 a longitudinal section through the complex model of plaster, with the tooth-stumps reconstituted in a reduced anatomical shape, with wax, made up of wax and gutta-percha;

FIG. 16 a, b, c, longitudinal sections through the complex model of plaster, after the removal of the complex of tooth-stumps;

FIG. 17 a longitudinal section through the plastic former, on the lid of which the complex of toothstumps is fastened;

FIG. 18 a longitudinal section through the negative (mould), from reversible hydrocolloid, of the tooth-stumps complex;

FIG. 19 a longitudinal section through the negative (mould), from reversible hydrocolloid, in which investment material was poured, in order to obtain the model of the tooth-stumps, of investment material;

FIG. 20 a, b longitudinal sections of the model realized from investment material, representing the tooth-stumps;

FIG. 21 a longitudinal section through the plaster complex model, on which slides the investment model of the coronary stumps, of investment material, on which adequate wax was applied, constituting thus the pattern of the crowns;

FIG. 22, u, b longitudinal sections of the model pattern, on which the casting rods has been applied;

FIG. 23 a a longitudinal section, through a complex of model-pattern, provided with a casting funnel, with a central canal, which complex is placed on the base of a former, on which the former cylinder has been applied, with the aim of obtaining the ,mould of investment material;

FIG. 23 b a transversal section through the BB plane in FIG. 23 a, of the model-pattern complex, after the realization of the mould; FIG. 24 a longitudinal section in the impression complex, in which one can see the impression of the stumps and the thermoplastic cone of the radicular impression, the stumps being covered with copper rings and thermoplastic material, over which the plaster super-impression has been taken;

FIG. 25 a longitudinal section of the impression complex, in which plaster was poured, comprising the area of the adjoining teeth;

FIG. 26 u, b longitudinal sections through the aggregate of the complex impression and of the extended model of hard plaster, after the pouring of the hard plaster into the impression of stumps and of the impression of the root canal, as well as of the edentate zone, with the aim of obtaining the complex model;

FIG. 27 u, h longitudinal sections of the complex model, after the removal of the mould of the complex impression of plaster, on which can be seen: the stumps covered with copper rings and thermoplastic material, as well as the thermoplastic cone of the root-canal impression, and the removal plaster model (b) of the adjoining teeth;

FIG. 28 a longitudinal section of the complex model, after the drawing out of the copper rings and the removal of the thermoplastic material, from the dental stump and of the root-canal impression;

FIG. 29 a, b longitudinal sections of the complex model, with the tooth-stumps reconstituted in a re duced anatomical shape, in the impression of the rootcanal being introduced a metallic taper dowel, with an internally threaded head, which dowel is fastened subsequently by means of a threaded-screw, to the lid of a former;

FIG. 30 a, h longitudinal sections as in FIG. 29 u, of the complex model of hard plaster, (a), fastened to the lid of a former (b), by means of a threaded screw, the lid being provided with a support, which contributes to the sustention of the complex model;

FIG. 31 a, I), c longitudinal sections through the negative (mould) (h), from reversible hydrocolloid, after the removal of the complex model of hard plaster;

FIG. 32 a longitudinal section through the negative (mould), from reversible hydrocolloid, in which an investment material has been poured, for the realization of the complex model duplicated in investment material;

FIG. 33 a longitudinal section through the complex model of investment material, after the removal of the metallic taper dowel, from the root-canal impression;

FIG. 34 a longitudinal section through the complex model of investment material and the removable plaster model of the adjoining teeth, on the coronary stump and the radicular stump of the complex model of investment material, being applied a' suitable wax (into the root-canal no wax is introduced), together with the pattern of the bridge body, united with the pattern of the crown and of the radicular retainer, realizing also a contact point with the adjoining teeth;

FIG. 35 a, I), c, d longitudinal sections through the modelpattern, on which were applied the casting rods (u) with the parts of no interest of the model of investment material removed, as well as the removable plaster model of the adjoining teeth ((1);

FIG. 36 a a longitudinal section through a model pattern complex, provided with a casting funnel, with a central canal, this complex being located on the base of a former, over which the former cylinder has been applied, with the aim of obtaining the mould of investment material;

FIG. 36 b a cross section through plane CC in FIG. 36, a, of the model-pattern complex, after the realization of the mould.

EXAMPLE I For the fabrication of dental bridges and full crowns, an impression of the stumps l is taken, in the dental office, according to the usual procedure. Over this impression, which contains copper tings 2, having inside thermoplastic material 3, a super-impression is taken, with plaster, forming a complex impression 4. The impression of the stumps, the alveolary crest zone, be tween the stumps constituting the edentate zone, as well as the impression of the adjoining teeth, can be obtained also with materials belonging to the silicone group. The realization of the working model, by the two impressing methods, is identical. Into the complex impression 4, isolated with a solution consisting of watter and soap, plaster 5 is poured in the adjoining teeth area 6. After the setting of the plaster 5, the complex impression 4 is isolated with the same solution and hard palster 7 is poured into the impression of the stumps 1, provided with copper rings 2 and thermoplastic material 3, comprising also the alveolary crest zone, between the stumps l, in order to obtain an extended model of the hemi-arch, and of the antagonist teeth (not represented in the drawing). After the stripping of the impression a complex model 8 of hard plaster 7 is obtained, with the slumps 1 covered with copper rings 2 and thermoplastic material 3, on which slides a removable model 9 of plaster 5, representing the adjoining teeth 6, which operation is followed by the removal of the copper ring 2, containing thermoplastic material 3, from the stumps 1, of the complex model 8. Subsequently, the stumps l of the complex model 8, of hard plaster 7, are fashioned into a reduced anatomical shape 10, with a wax consisting of gutta-percha and pink modelling wax, in ratio of 3.3 g pink wax per 1 g of gutta-percha. The cervical zone 11 of stumps 1 not being fashioned on a portion of 1-1.5 mm from the cervical edge 11 of stumps l and not realizing contact points, between stumps 1 and the adjoining teeth 6, thus leaving a space S of about 0.4 mm to the adjoining teeth 6 and to the antagonistic teeth (not shown in the drawing).

The removable model 9 is removed from the complex model 8 of hard plaster 7, with the stumps 1 fashioned into a reduced anatomical shape 10, with wax made up of gutta-percha and wax, in order to introduce it into a vessel with cold water, where it is left for 10 to 15 minutes. Then the complex model 8 is removed from the water and fastened to the lid 12, which is introduced in a former 13, where a negative (mould) of the complex model 8 is obtained, in reversible hydrocolloid 14, by pouring into the former 13, the reversible hydrocolloid 14, molten at C and tempered to 45-50C. The former 13, together with the reversible hydrocolloid 14, is immersed into cold water. After cooling, the lid 12, of the former 13, is drawn out and the complex model 8 of hard plaster 7 is removed from the hydrocolloid 14. lnto the negative (mould) 15, realized from reversible hydrocolloid 14, investment material 16, suitable for chrome-cobalt alloys, is poured, at the usual ratios of powder and water, mixed for one minute, on a vibrating table. The investment material 16 sets in about 20 minutes, in the course of which occurs also the hygroscopic expansion, after which a model 17 of investment material 16 is taken out carefully, which model is introduced into a furnace, where it is left for 15 minutes, at a temperature of 220C, at which the initial thermal dilatation is taking place.

The model 17 of investment material 16, removed from the furnace, is immersed for 15 seconds into a wax bath, heated to C. After the cooling of model 17 of investment material 16, the pattern is fashioned in wax of adequate thickness, applying over the stumps a wax strip 18, of 0.4 mm thickness, while on the occlusal faces, too, a wax disc of the same thickness.

The pattern is completed with blue wax, added dropwise for the reproduction of the occlusal relief and of the proximal contact points 19, giving the pattern of the crowns an anatomical shape. The pattern of the bridge body 20 is fashioned in blue wax, using the usual technique.

Subsequently, on the wax pattern of the future onepiece cast bridge 21, are applied the casting rods of wax 22, whose number and ramifications depend on the pattern that is to be cast.

Afterwards, the base of model 17, of the investment material 16, with the wax pattern of the future cast bridge 21, is attached with wax to the lid of a cylindrical former 23, after which a former of the casting funnel 24, provided with a wax canal 25, is applied on the upper part of the wax casting rods 22. Then the model pattern complex of the future cast bridge 21 is invested, with investment material 16, obtaining mould 26, which is heated, slowly in the beginning, to 300C, in order to enable the trickling down of the wax and drying of the investment material, after which it is further heated to 9001,000C, in order to bring about a thermal dilatation of the investment material 16. Subsequently, the chrome-cobalt alloy, melted previously, is cast into mould 26, the casting being effected with the known apparatus, based on centrifugal force.

Possible small adjustments of the crowns, that form the constituting elements of the one-piece cast dental bridges for their adaptation to the stumps 1, of the complex model 8, of hard plaster 7, are made with mounted and unmounted abrasive stones.

EXAMPLE ll In the case of completely metallic or mixed semi physiognomical dental one-piece cast dental crowns, with controlled thicknesses, made of chrome-cobalt alloy, the methods are identical, excepting the fact that all is worked on mobile stumps 27, of hard plaster 7, fastened on plastic supports 28, provided with metal rods 29, which slide in an extended model 8, of plaster 5.

The negative (mould) of reversible hydrocolloid 14 is obtained by fastening the complex on lid 30, which is introduced into the former 31. The lid 30 of the former 31, is provided with holes r, that permit the penetration of the metal rod 29 of the plastic support 28, in order to give the base of the plastic support a rigorously vertical position.

EXAMPLE III In the case of one-piece cast bridges, with controlled thicknesses, made of chrome-cobalt alloy, whose constituting elementas are one or several corono-radicular retainers and full crowns, the impressions of the stumps and of the root-canal are taken, in the dental office, under the known conditions. Over this impression, which contains copper rings 2, having in the interior thermoplastic material 3 and a cone of thermoplastic material 3, which permits the taking of the impression of the root-canal, a super-imposed is taken with plaster, forming the complex impression 4.

For the realization of the working model, one uses the methods described for dental bridges, in example I, that is, obtaining after the stripping of the superimpression, a complex model 8, of hard plaster 7, with the stumps covered with copper rings 2 and thermoplastic material 3, with the impression of the canal 32, on which slides a removable model 9 of plaster 5, representing the adjoining teeth 6, which operation is followed by the removal of the copper rings 2, which contain thermoplastic material 3, from stumps 1, as well as the cone of thermoplastic material 3, which enables the realization of the impression of the root-canal 32, on the complex model 8.

Subsequently, the tooth stump 1, on the complex model 8, which will form the coronary constituting elements, is fashioned into a reduced anatomical shape 10, with a wax consisting of gutta-percha and pink wax, the cervical zone 11 of the stump 1 remaining unfashioned, on a portion of 1-1.5 mm, from the cervical edge 11 of the tooth stump 1.

The complex model 8, of hard plaster 7, with the impression of the root-canal 32 and tooth stump 1, fashioned in a reduced anatomical shape 10, is isolated with cold water, in order to avoid the sticking of the wax, that will be introduced into the root-canal 32, after which, in the same root-canal, a metallic taper dowel with an internally threaded head 33, is introduced, which dowel pressure the wax against the walls of the root-canal 32, remaining fixed in a rigurously vertical position.

The removable model 9, of plaster 5 is removed from the complex model 8, of hard plaster 7. The complex model 8, whose tooth stump l is fashioned in a reduced anatomical shape 10, together with the metallic taper dowel, with an internally threaded head 33, is fastened, by means of a threaded screw 34 to the lid 35, of a former 36. The lid 35 is provided with an orifice f. which is slidable in a slit, which contributes to the fixing of the metallic dowels, as well as with a support d, in the interior of which a screw 6 is threaded, which helps to sustain the complex model 8 of hard plaster 7.

The complex model 8, of hard plaster 7, fastened to the lid 35, is introduced into the former 36. After the isolation of the model in cold water, it is duplicated in reversible hydrocolloid 14, Obtaining a com lex model 37, of investment material 16, by means of a negative (mould) 15, of reversible hydrocolloid 14, into which is poured the investment material 16, which permits a hygroscopic expansion. The investment material 16 is left, for about 45 minutes, until it sets, after which it is carefully detached from the reversible hydrocolloid 14, resulting finally a complex model 37, of investment material 16.

To this end, the block off reversible hydrocolloid 14 is removed, together with the lid 35, from the former 36, followed by the unscrewing of the screw 34, which served for the fastening of the taper dowel 33, introduced into the impression of the root-canal 32.

The reversible hydrocolloid 14 is cut into slices and the complex model 37 of investment material 16 is disengaged very carefully.

The metallic taper dowel 33 is removed by heating from the impression of the root-canal 32, of the complex model 37, of investment material 16. The model of investment material thus obtained receives then the same treatment as in the case of dental bridges and dental crowns, including casting, that is, the pattern of the radicular retainer is modelled with wax 18, without introducing wax into the root-canal impression 32; then follows the fashioning of the crown pattern, with wax 18, followed by the fashioning of the bridge body 20, the application of the casting rods 22 and the investing of the model-pattern complex 38 into investment material 16.

For the realization of mould 26, into which the chrome-cobalt alloy is casted, the method described in the case of dental bridges, in example I, is used.

This method presents the following advantages:

it permits the burning of the porcelain (ceramic) on the dental bridges, as well as on the dental crowns, realized from one-piece and made of chrome-cobalt alloys;

it replaces the alloys with a 50% content of gold, platinum, palladium, used with the aim of permitting the burning of the porcelain on dental works and on dental crowns;

it enables the fabrication of dental bridges, without adjustments, at the level of the occlusal surface, at 10 the moment of its adaptation in the buccal cavity, due to the fact that the dental stumps have a fixed position on the complex model of hard plaster, replacing the small removable model, comprising the stumps area and the alveolary crests zone, by a removable model, comprising the adjoining teeth;

the dental full crowns, executed on mobile stumps of hard plaster, fastened to plastic supports, enable an adaptation without adjustments at the level of the occlusal surface;

it enables the fabrication of dental bridges, from one piece, with controlled thicknesses, from chromecobalt alloy, whose constituting elements are radicular retainers, crowns and the bridge body, thus obtaining a physiognomical effect, in the case of the restoration of frontal and lateral edentations.

We claim:

1. A method of making a dental prosthesis to be received in the buccal cavity in the mouth area having an adjoining tooth region, comprising the steps of:

a. forming a negative impression of said area including the adjoining tooth region;

b. casting a positive rigid adjoining-tooth model from the negative impression formed in step (a);

c. casting a rigid positive impression of the negative impression formed in step (a) and adapted to removably engage said adjoining-tooth model;

d. reproducing the positive impression of step (c) in investment material to form a positive investment model adapted to removably engage said adjoining tooth model;

e. joining said adjoining-tooth model with said investmentmodel and forming a prothesis shape therein in wax immediately adjacent said adjoining-tooth model; and

f. investment-casting a molten metal into the space occupied by said wax, said mouth area having at least one tooth stump and said positive impression and said positive investment model having respective tooth-stump formations corresponding to the tooth stump in said mouth area, said prosthesis shape being formed in step (e) at least in part by applying a thin strip of wax around said toothstump formation of said investment model, and applying a wax disk corresponding to the occlusal surface of a tooth formation of said positive investment model and shaping the wax on said toothstump' formation of the latter substantially to contact said adjoining-tooth model, said tooth stump of said mouth region being provided with a copper ring containing a thermoplastic material for entrainment in said negative impression in step (a).

2. The method defined in claim 1 wherein said strip has a thickness of about 0.4 mm and the positive impression of step (c) is reproduced in investment material in step (d) by the steps of:

d fixing said rigid positive impression to a holder;

d casting a settable hydrocelloid around said rigid positive impression of said holder;

d setting the hydrocolloid of step (d and removing said positive impression to form a negative hydrocolloid mold;

d casting said investment material in said negative hydrocolloid mold; and

d,-,. removing said hydrocolloid from the investment material cast therein.

3. The method defined in claim 1 wherein said investment model corresponds to a tooth stump formed with the prosthesis shape and is inserted into a body formed with said adjoining-tooth mold.

4. The method defined in claim 1 wherein said positive impression is formed with a root-canal impression, said method further comprising the steps of:

introducing wax into said root-canal impression:

introducing a taper dowel into said root-canal impression to press the wax into contact with the walls thereof; and

thereafter casting a reproduction of said root canal in said metal in step (f) by displacement of the wax of said root-canal impression.

5. The method defined in claim 1 wherein the metal cast in step (f) is a chromium-cobalt alloy. 

1. A method of making a dental prosthesis to be received in the buccal cavity in the mouth area having an adjoining tooth region, comprising the steps of: a. forming a negative impression of said area including the adjoining tooth region; b. casting a positive rigid adjoining-tooth model from the negative impression formed in step (a); c. casting a rigid positive impression of the negative impression formed in step (a) and adapted to removably engage said adjoining-tooth model; d. reproducing the positive impression of step (c) in investment material to form a positive investment model adapted to removably engage said adjoining tooth model; e. joining said adjoining-tooth model with said investment model and forming a prothesis shape therein in wax immediately adjacent said adjoining-tooth model; and f. investment-casting a molten metal into the space occupied by said wax, said mouth area having at least one tooth stump and said positive impression and said positive investment model having respective tooth-stump formations corresponding to the tooth stump in said mouth area, said prosthesis shape being formed in step (e) at least in part by applying a thin strip of wax around said tooth-stump formation of said investment model, and applying a wax disk corresponding to the occlusal surface of a tooth formation of said positive investment model and shaping the wax on said tooth-stump formation of the latter substantially to contact said adjoining-tooth model, said tooth stump of said mouth region being provided with a copper ring containing a thermoplastic material for entrainment in said negative impression in step (a).
 2. The method defined in claim 1 wherein said strip has a thickness of about 0.4 mm and the positive impression of step (c) is reproduced in investment material in step (d) by the steps of: d1. fixing said rigid positive impression to a holder; d2. casting a settable hydrocelloid around said rigid positive impression of said holder; d3. setting the hydrocolloid of step (d2) and removing said positive impression to form a negative hydrocolloid mold; d4. casting said investment material in said negative hydrocolloid mold; and d5. removing said hydrocolloid from the investment material cast therein.
 3. The method defined in claim 1 wherein said investment model corresponds to a tooth stump formed with the prosthesis shape and is inserted into a body formed with said adjoining-tooth mold.
 4. The method defined in claim 1 wherein said positive impression is formed with a root-canal impression, said method further comprising the steps of: introducing wax into said root-canal impression: introducing a taper dowel into said root-canal impression to press the wax into contact with the walls thereof; and thereafter casting a reproduction of said root canal in said metal in step (f) by displacement of the wax of said root-canal impression.
 5. The method defined in claim 1 wherein the metal cast in step (f) is a chromium-cobalt alloy. 